kevs,

Take a look at SendStuffNow.

A Macworld article: SendStuffNow offers secure, managed file delivery.

I am not sure you will be able to find a "good" and "big" online file sharing service which is free and meets your other requirements.

Consider the costs of the hardware, the software, the bandwidth for uploads and downloads, and the staff to administrate and troubleshoot the site / service.

Back up everything you can't afford to lose: documents, mail, movies, music, photos, and other data and settings.